The present invention relates to radiant heaters, and particularly to an infrared heater apparatus. More particularly, the present invention relates to an infrared heater apparatus for use on a thermal support device for maintaining a patient, such as an infant, at an appropriate temperature.
Incubators and radiant warmers have both been used to maintain the appropriate body temperature of small or premature infants. Radiant warmers provide for continuous and open access to an infant to accommodate a high frequency of intervention by the caregiver. Radiant warmers transfer heat to the patient via radiant heat transfer, typically from infrared heaters which emit infrared energy that is absorbed by the patient. The infrared heater is usually mounted to a support which is suspended above the patient support surface of the radiant warmer. See, for example, U.S. Pat. No. 5,162,038.
An incubator provides a generally transparent enclosure within which heated air is circulated to minimize the heat loss of the patient. In addition, heat is transferred to the patient via convective heat transfer. Incubators are typically provided with a large access door to allow for placement or removal of the infant in the incubator as well as supplemental access ways such as hand ports or small entry doors to permit routine care of the infant while minimizing heat loss from the incubator and the infant.
Incubators protect patients such as premature infants from exposure to ambient nursery contaminants in the form of noise and unfiltered air. Incubators provide mechanisms for filtering the air and raising the oxygen level within the incubator, as well as humidification mechanisms to control the relative humidity within the incubator. Patients such as infants or premature infants can often benefit from an oxygen-enriched atmosphere, because it reduces the amount of energy that must be expended by the patient in respiration, allowing the patient to maintain a lower metabolic rate. Patients with a variety of conditions, such as infections, elevated temperatures, or reduced amounts of hemoglobin, benefit from the oxygen-enriched atmosphere within the incubator.
U.S. Pat. No. 5,453,077 discloses an exemplary infant thermal support device that can function as either an incubator, a radiant warmer, or both. In the infant thermal support device of the '077 patent, air curtains cooperate with a patient-support surface to define a patient space that is protected from disturbances from outside of the patient space. The air curtains define an effective barrier to atmospheric influences outside of the patient space so that the patient space is generally unaffected by changes in the environment surrounding the patient thermal support device. At the same time, the patient thermal support device can be operated so that there are no physical barriers between the patient and the caregiver, providing the caregiver with continuous and open access to the patient even when the air curtains are in place.
The patient thermal support device of the '077 patent also includes an infrared radiant heater connected to the canopy to transfer heat to the patient via radiant heat transfer. The infrared radiant heater cooperates with the patient's own warmth, the warmed air that escapes the manifold to warm the patient support surface, and the warmed air of the air curtains delivered to the patient, to maintain the desired thermal environment for the patient. The radiant heater can help to achieve and maintain the desired patient temperature when neither the patient nor the warmed air are sufficient for attaining and maintaining the desired patient temperature.
The region of the electromagnetic radiation spectrum having wavelengths between about 760 and 1,000,000 nanometers (nm) is considered infrared radiant energy.
Infrared A band includes wavelengths ranging from about 760-1,400 nm. Infrared B band includes wavelengths ranging from about 1,400-3,000 nm. Infrared C band includes wavelengths ranging from about 3,000-100,000 nm.
The infrared heater apparatus of the present invention is designed to minimize infrared radiation in the infrared A band. The infrared heater of the present invention emits substantially all of its radiant energy within the infrared B and C bands of the radiation spectrum.
Typical infrared heaters operate at very high temperatures ranging from about 1,100-1,200.degree. C. and emit a red glow during operation. The glowing tube of a conventional infrared heaters can distort the color appearance of a child. Therefore, it is sometimes difficult to take an accurate color reading of an infant situated below a conventional infrared heater. The heater of the present invention operates at a substantially reduced temperature of about 300.degree. C. to about 500.degree. C. and does not glow. This facilitates taking accurate color readings of infants. The cooler heater of the present invention also reduces risks to the caregiver.
Since surface temperatures of the heater apparatus of the present invention are reduced, two such heaters are typically used in a patient thermal support device of the present invention to provide sufficient radiant energy to the support surface. Alternatively, a single heating element may be used having a larger diameter to produce larger emitting surface.
A common type of infrared heater used in infant radiant warmers is a "quartz tube" type, which comprises an infrared heat source contained within a quartz tube. An advantage to the quartz tube is that it is relatively transparent to infrared heat, allowing for rapid warm-up and cool-down of the infrared heater. Current quartz heaters are not sealed for use in an oxygen-enriched environment.
Another common type of heater used in infrared radiant warmers is known as a Cal-Rod.TM. type heater. These heaters have a wire heating element inside a metal sheath that is then packed densely with magnesium oxide. Cal-Rod.TM. type heaters reduce the potential for contact between the heating element and oxygen-enriched atmosphere.
However, the Cal-Rod.TM. heater provides only one seal around the heating element. If this single seal fails, the heating element would be exposed to the atmosphere. The Cal-Rod.TM. heater also has a relatively high thermal mass, requiring rather long warm-up and cool-down times when compared to the quartz heater design.
The present invention provides the quick warm-up and cool-down times of the quartz tube type heater and the safe operation in an oxygen-enriched atmosphere feature of the Cal-Rod.TM. type heater. The present invention provides an infrared heating device that minimizes the potential for contact between the heating element and the oxygen-enriched atmosphere, while also providing a relatively low thermal mass to allow for relatively short warm-up and cool-down times. The present invention also reduces emission of infrared A band wavelengths.
According to one aspect of the present invention, a radiant heater apparatus includes a heating element which generates radiant energy. The heating element has first and second terminals. The apparatus also includes an inner tube configured to surround the heating element. The inner tube includes first and second ends. The inner tube is substantially transmissive to radiant energy. The apparatus further includes an outer tube surrounding the inner tube. The outer tube has an inner surface, an outer surface, and first and second ends. The inner surface of the outer tube is absorptive to radiant energy, and the outer surface of the outer tube is emissive to radiant energy so that radiant energy from the heating element passing through the inner tube is absorbed and re-emitted from by outer tube.
In the illustrated embodiment, the outer tube is formed from metal such as stainless steel. The inner and outer surfaces of the outer tube are coated with an oxide material. The inner tube is formed from a quartz material. The heating element generates radiant energy with wavelengths having a first average length and the outer tube emits radiant energy with wavelengths having a second average length greater than the first average length.
In one illustrated embodiment, at least one spacer is located between the inner tube and the outer tube. Illustratively, the at least one spacer includes first and second silicone grommets located between the inner and outer tubes adjacent the first and second ends of the inner and outer tubes, respectively. First and second end caps coupled to the first and second ends of the inner tube, respectively.
In another illustrated embodiment for use in an oxygen enriched environment, first and second plugs are configured to be inserted into the first and second ends of the outer tube, respectively, to engage the inner surface of the outer tube and the inner tube to provide a seal between the outer tube, the inner tube, and the terminals of the heating element. First and second end caps are configured to be coupled to the first and second ends of the outer cylinder, respectively, to seal the outer cylinder and the first and second terminals of the heating element. The Association for Advancement of Medical Instruments (AAMI) requirements for heaters used in an oxygen-enriched environment require two separate fault conditions to occur before the heating element is exposed to the atmosphere.
The outer tube and the first and second end caps are illustratively made from a metal material. The first and second end caps are welded to the outer tube.
According to another aspect of the present invention, a patient warmer apparatus is provided for heating a patient on a patient support surface. The apparatus includes an infrared heater which emits a radiant energy output having wavelengths substantially within the infrared B and infrared C bands to minimize radiant energy emitted in the infrared A band.
Illustratively, the infrared heater emits radiant energy having a center spectrum with wavelengths between about 3,000-5,000 nm. The radiant heater has an output temperature of less than 1000.degree. C., and illustratively between about 300.degree. C. and about 500.degree. C.
According to yet another aspect of the present invention, a patient thermal support apparatus includes a base, a patient support surface on the base, and a warmer module coupled to the base spaced apart from the patient support surface. The warmer module includes first and second infrared heaters which emit infrared radiant energy, the first and second heaters each having an operating temperature less than 1000.degree. C. Illustratively, the first and second radiant heaters each have an output temperature of about 300.degree. C. to about 500.degree. C. and do not emit a red glow like conventional infrared heaters.
Illustratively, the first and second radiant heaters each emit a radiant energy output having wavelengths substantially within the infrared B and infrared C bands to minimize radiant energy emitted in the infrared A band. The first and second infrared heaters each emit radiant energy having a center spectrum with wavelengths between about 3,000-5,000 nm.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.